1. Field of the Invention
The present invention relates to a small-size current sensor capable of sensing a change in current flowing in a conductor with high sensitivity.
2. Description of the Related Art
Generally, to accurately detect weak control current flowing in control equipment, a method of connecting resistors in series in the circuit and measuring a voltage drop in the resistors is used. In this case, however, a load different from a control system is applied and there is the possibility that an adverse influence is exerted on the control system. Consequently, a method of indirectly measuring control current by detecting the gradient of a current magnetic field generated by the control current is used. A concrete example is a method of winding a line to be measured around a toroidal core and detecting a magnetic flux generated in the center portion of the toroidal core by supplying control current to the measurement line.
With respect to a current sensor realizing the method, problems such as difficulty of realizing miniaturization and insufficient linearity or high frequency responsiveness are pointed out. To solve the problems, a current sensor in which a giant magnetoresistive element (hereinbelow, GMR element) producing giant magnetoresistive effect is disposed in the current magnetic field, and the gradient of the current magnetic field is detected has been proposed (refer to, for example, U.S. Pat. No. 5,621,377). In a current sensor using such a GMR element, detection sensitivity and responsiveness improves and detection characteristics which are stable against a temperature change are obtained.
Recently, a current sensor capable of detecting weaker current and having a more compact general configuration is being demanded. In a conventional current sensor, however, a GMR element is provided so as to be adjacent to a line to be measured in an in-plane direction, so that it is difficult to detect weak current and it is disadvantageous from the viewpoint of miniaturization.